Electrostatic interaction between dissimilar colloids at fluid interfaces

Abstract

The electrostatic interaction between two nonidentical, moderately charged colloids situated in close proximity of each other at a fluid interface is studied. By resorting to a well-justified model system, this problem is analytically solved within the framework of linearized Poisson-Boltzmann density functional theory. The resulting interaction comprises a surface and a line part, both of which, as functions of the interparticle separation, show a rich behavior including monotonic as well as nonmonotonic variations. In almost all cases, these variations cannot be captured correctly by using the superposition approximation. Moreover, expressions for the surface tensions, the line tensions and the fluid-fluid interfacial tension, which are all independent of the interparticle separation, are obtained. Our results are expected to be particularly useful for emulsions stabilized by oppositely charged particles.

Electrostatic pair-interaction of nearby metal or metal-coated colloids at fluid interfaces

“…As expected, the interfacial tension depends only on the properties of the two fluid media and not on any plate properties. Consequently, the expression for γ 1,2 does not differ from what one obtains for plates with constant surface charge densities [53].…”

“…( 13) vanish except for the last term, i.e., τ. Therefore, in this limit ω τ (L) stays finite unlike what one observes for constant charge boundary condition [50,53]. Using the relation ∞ n=1,3,...…”

“…Most of the few recent efforts [50][51][52][53][54] targeted toward addressing the short inter-particle separations have considered particles with constant surface charge densities, which, at a simplistic level, describes dielectric or insulating particles the best [55,56]. Conductive metal particles, on the other hand, are characterized by constant surface potentials [56].…”

“…First, the short inter-particle separation is exploited to treat the particles as flat plates by ignoring their curvatures. This assumption, motivated by the Derjaguin approximation, has been used before in this context as well [50,51,53]. Second, we assume the fluid-fluid interface to be flat as interfacial deformations are usually negligible for smooth particles up to a few micrometers in size [35,[69][70][71].…”

Electrostatic interaction of particles trapped at fluid interfaces: effects of geometry and wetting properties

“…It has been shown that in this case the linearization of the Poisson-Boltzmann (PB) theory is applicable [21]. Recent studies, directed towards the opposite limit of small inter-particle separations, have been performed within the linearized PB theory [22][23][24] or by considering a flat plate geometry [22,24,25] in order to simplify the problem. Whereas the former approximation is often violated at short separations, the latter represents the ideal situation of a contact angle of exactly 90 • and the absence of particle curvature.…”